Stainless steel sheets have been widely used as heat-resistant uses. For example, stainless steel is used in an exhaust system of an automobile, which is required to have corrosion resistance performance in a high-temperature corrosive environment. Since stainless steel is expensive, replacement with aluminum plating, which is less expensive and is excellent in heat resistance, is pursued; however, since aluminum plating has only insufficient corrosion resistance in an environment in which it is exposed to NOx and SOx, such as around a muffler, most of the materials are still stainless steel.
Thus, the present inventors have worked toward the development of heat-resistant Ni—Cr alloy plating using Ni and Cr that does not dissolve in nitric acid or sulfuric acid, with the purpose of providing a material that is inexpensive and is excellent in high-temperature corrosion resistance and corrosion resistance in NOx and SOx environments, and that can take the place of stainless steel.
As methods for producing Ni—Cr alloy plating, various technologies of performing thermal diffusion treatment on two-layer plating of Cr and Ni are disclosed.
For example, Patent Literature 1 mentions that Cr plating is performed on a steel sheet in the first place and Ni plating is performed on the Cr plating, then the steel sheet is heat-treated in a non-oxidizing atmosphere at 600° C. to 910° C. for 60 seconds to 20 hours, and thereby a component that is made to resemble 18-8 stainless steel is obtained. Further, Patent Literature 2 mentions that Cr plating and Ni plating are performed on a steel sheet, then the steel sheet is heat-treated in a molten salt bath at 750 to 900° C. for 1 to 4 hours, and thereby a component that is made to resemble 18-8 stainless steel is obtained. Further, Patent Literature 3 mentions that Cr plating is performed on a steel sheet in the first place and Ni plating is performed on the Cr plating, then the steel sheet is heat-treated, and thereby plating including a Ni—Cr alloy layer and a Cr—Fe—Ni alloy layer is obtained.